Genetic and environmental factors are studied in 43 matched pairs of schizophrenics and control subjects adopted in the Danish Provinces outside of Copenhagen, along with their 582 adoptive and biological sibs and half-sibs. In addition to making diagnoses, the interviewers collect data on social, medical, and psychiatric hospitalization history, mental status, schizotypal personality, thought disorder, communication deviance, blunted affect, visual tracking, birth complications, and platelet monoamine oxidase. Research strategies are aimed at distinguishing between environmental and genetic parental influences and determining if environmental factors associated with schizophrenia are causes or effects of the disorder. Families with a high density of schizophrenia are studied to determine possible etiological subtypes of schizophrenia. Schizophrenics and nonschizophrenics likely to be carring the same genetic predisposition for schizophrenia are compared.